Previous work in this laboratory has described the absorption and tissue distribution of halogenated hydrocarbons and the importance of metabolism to the excretion of these compounds. The results of current studies demonstrate that adjacent unsubstituted carbon atoms in the meta-para positions of polychlorinated biphenyls (PCBs) facilitate their metabolism via arene oxide intermediates and results in greater binding to subcellular macromolecules. Other current work demonstrates that the adipose tissue is not a well mixed pharmacokinetic compartment and that this fact may result in inaccurate extrapolation of disposition data from acute to chronic studies.